Conventional electronic fuel injection systems use an electrically powered pump to supply fuel to the fuel injectors. The pump is controlled to operate at a constant speed. For newer pumping systems which do not return fuel to the fuel tank, i.e., an electronic returnless fuel pump, the absence of a return line from the fuel rail to the fuel tank may result in slightly higher fuel rail temperatures.
This may have the effect of changing physical characteristics of both the fuel and the fuel injector, such as causing the density of the fuel to decrease, and the electro-mechanical response of the fuel injector to be slower.
In certain types of fuel delivery systems, an adaptive algorithm is utilized to monitor and compensate for overall fueling error to the combustion engine. These errors are typically introduced by unit-to-unit variability in system components, as well degradation of such components as a result of aging or contamination. Adaptive systems usually employ an oxygen sensor, such as a heated exhaust gas oxygen (HEGO) sensor, to provide a feedback signal to the control algorithm, where the difference between a commanded air-to-fuel (A/F)ratio and an actual A/F ratio is then determined to generate the needed modification factor. These modification results are stored in a large keep-alive-memory (KAM) type memory arrangement, which is constantly updated in accordance with the detected error in A/F ratio.
While the adaptive process will ultimately deliver the desired fuel mass regardless of fuel temperature of injector response, such constant corrective action undesirably occupies a portion of range reserved by the adaptive process for unforeseeable in-use errors, thereby making the system less capable of providing other corrections.
Therefore, a need exists for a fuel delivery control arrangement which can compensate for rail temperature without taxing a vehicle's adaptive fuel delivery control process.